Analysis of three-phase, three-level VSIs is done for high-power high-voltage applications. Complete Space Vector Modulation (SVM) algorithm is developed for a three-phase, three-level converter. Special attention is given to minimization of output ripple and voltage balance of the dc-link input capacitors. Verification of the proposed SVM algorithm is done by computer simulation. Comprehensive small-signal modeling of the three-level converter with a resistive load is developed the first time. Steady-state solutions reveal that the voltage across dc-link input capacitors is constant at the half of the dc-link voltage. / Master of Science

Switched reluctance motor has features like robust structure, low cost, and wide speed extension range over conventional induction and synchronous motors. These features make it a promising choice for many applications from electric vehicle to aerospace industry. However, due to its silent structure, the characteristics of switched reluctance motor are highly nonlinear. The nonlinearity makes it difficult to control and results in degraded performance such as high torque ripple and acoustic noise compared with conventional induction machine or synchronous machine. New power converters and control methods have to be developed to improve its performance. In order to reduce the current ripple and torque ripple, a novel three-level converter for switched reluctance motor is proposed. The operation modes and modulation method are presented in detail. Simulation and experimental results show that compared to conventional two-level converter, the proposed three-level converter is able to reduce current ripple, torque ripple and acoustic noise significantly without increasing cost. A fast and accurate current controller is essential for the torque control of switched reluctance motor. An adaptive current controller for the three-level converter is developed to avoid the performance degradation caused by manufacture inconsistency. This controller has the ability to adjust its parameters according to the specific motor it drives. Fast dynamic and high accuracy could be achieved through parameter adaption. In order to reduce the cost, and compete with the well-developed sensorless brushless DC and induction motor drive system, a new position sensorless control method for switched reluctance motor is proposed. This method is effective under both low speed operation and high speed operation. It can start with heavy load. It does not have to align the machine before start up as what is needed for many sensorless brushless DC drive systems. The proposed converter and control methods are all verified by simulation and experimental results. / Thesis / Doctor of Philosophy (PhD)

One of the requirements for the next generation of power supplies for distributed power systems (DPSs) is to achieve high power density with high efficiency. In the traditional front-end converter based on the two-stage approach for high-power three-phase DPSs, the DC-link voltage coming from the power factor correction (PFC) stage penalizes the second-stage DC/DC converter. This DC/DC converter not only has to meet the characteristics demanded by the load, but also must process energy with high efficiency, high reliability, high power density and low cost. To meet these requirements, approaches such as the series connection of converters and converters that reduce the voltage stress across the main devices have been proposed. In order to improve the characteristics of these solutions, this dissertation proposes high-efficiency, high-density DC/DC converters for high-power high-voltage applications. In the first part of the dissertation, a DC/DC converter based on a three-level structure and operated with pulse width modulation (PWM) phase-shift control is proposed. This new way to operate the three-level DC/DC converter allows soft-switching operation for the main devices. Zero-voltage switching (ZVS) and zero-voltage and zero-current switching (ZVZCS) soft-switching techniques are studied, analyzed and compared in order to improve the characteristics of the proposed converter. This results in a series of ZVS and ZVZCS three-level DC/DC converters for high-power high-voltage applications. In all cases, results from 6kW prototypes operating at 100 kHz are presented. In addition, with the ultimate goal of improving the power density of the DC/DC converter, a study of several resonant DC/DC converters that can operate at higher switching frequencies is presented. From this study, a three-element ZVS three-level resonant converter for applications with wide input voltage and load variations is proposed. Experimental results at 745 kHz obtained without penalizing the efficiency of the PWM approaches are presented. The second part of the dissertation proposes a quasi-integrated AC/DC three-phase converter that aims to reduce the complexity and cost of the traditional two-stage front-end converter. This converter improves the complexity/low-efficiency tradeoff characteristics evident in the two-stage approach and previous integrated converters. The principle of operation for the converter is analyzed and verified on a 3kW experimental prototype. / Ph. D.